1. Field of the Invention
This invention relates to a method for hydroxylation of phenol and, more particularly, to a method for catalyzing the hydroxylation of phenol by using solid catalyst containing cobalt.
2. Description of Related Art
In accordance with the variable properties of resorcinol, hydroquinone and pyrocatechol, they are important chemical products which can be applied in various industries, such as electronics, medicine, and chemistry. They are employed in organic synthesis industry such as developer, polymerization inhibitor, skin whitening agent, antioxidant, germicidal agent, rubber additive, electroplating additive, light stabilizer, dye, spice reductant, special ink and the like.
In general, hydroquinone and pyrocatechol are prepared by hydroxylation of phenol using hydrogen peroxide as oxidant with the addition of catalyst to enhance the progression of hydroxylation. At present, zeolite is used as catalyst for the hydroxylation of phenol and it provides the advantage of easily separating catalyst and product after the reaction. The more commonly utilized zeolites are TS-1, ZSM-5, β and Y-type molecular sieve, in which the commercially available TS-1 type molecular sieve has better effects.
U.S. Pat. No. 4,396,783 discloses a titanium-silicon solid catalyst added with a modified metal for use in the hydroxylation of phenol. However, the patent actually used iron, chromium or vanadium to carry out the modification and the yield of diphenol prepared by the hydroxylation of phenol is 8.58% and the highest ratio of hydroquinone and pyrocatechol (H/P) is 0.6.
U.S. Pat. No. 5,399,336 discloses the synthesis of a silicon catalyst (S-1) containing stannum and zirconium, and further discloses performing the hydroxylation of phenol with hydrogen peroxide (70 wt %). The yield of diphenol is 27.5% using S-1 catalyst containing stannum. The yield of diphenol is 28% using S-1 catalyst containing zirconium. Both of these not only have the safety concerns, but also fail to significantly increase the yield of diphenol.
UK Patent No. 2116974 discloses a TS-1 solid catalyst having MFI structure as catalyst for the hydroxylation of phenol. The obtained H/P ratio is 1, and the selectivity of hydrogen peroxide is 73.9%. Likewise, European Patent No. 0266825 discloses a TS-1 solid catalyst containing gallium for carrying out the hydroxylation of phenol. The solid catalysis rate of hydrogen peroxide is 74.7%, and the H/P ratio is 0.79.
From the above, the application of solid catalyst in the conventional techniques for the hydroxylation of phenol still has low H/P ratio of diphenol product and low selectivity of hydrogen peroxide. Besides, the conventional techniques do not employ the solid catalyst containing cobalt in the hydroxylation of phenol.
Therefore, the development of a solid catalyst to increase H/P ratio of the products, selectivity of diphenol, and selectivity of hydrogen peroxide has become an urgent issue to be solved.